A typical vane-type camshaft phaser for changing the phase relationship between a crankshaft and a camshaft of an internal combustion engine generally comprises a plurality of outwardly-extending vanes on a rotor interspersed with a plurality of inwardly-extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. Engine oil is selectively supplied to one of the advance and retard chambers and vacated from the other of the advance and retard chambers by a phasing oil control valve in order to rotate the rotor within the stator and thereby change the phase relationship between the camshaft and the crankshaft. One such camshaft phaser is described in United States Patent Application Publication No. US 2016/0024978 to Lichti, hereinafter referred to as Lichti.
Lichti teaches a camshaft phaser attachment bolt which serves to attach the camshaft phaser to the camshaft and which also serves as a valve body having a valve bore within which a valve spool is axially displaced in order to open and close passages in the camshaft phaser attachment bolt. Consequently, axial movement of the valve spool directs oil to fill or vacate the advance and retard chambers in the proper combination to advance and retard the timing. Lichti teaches that advance and retard passages, which are circular in cross-section, extend radially outward from the valve bore to grooves on the outer circumference of the camshaft phaser attachment bolt. Consequently, when corresponding lands of the valve spool begin to open the advance and retard passages, flow increases gradually due to the geometry of the advance and retard passages being circular and cross-section interacting with an annular edge of the valve spool. While this gradual increase in flow may be desirable for providing greater control stability of the camshaft phaser, the maximum flow rate is limited to the flow area of the advance and retard passages that is uncovered by the valve spool, thereby limiting the phasing rate of the camshaft phaser.
Another such camshaft phaser is described in United States Patent Application Publication No. US 2012/0152195 to Schulze et al., hereinafter referred to as Schulze et al. In contrast to Lichti, Schulze et al. teaches a camshaft phaser attachment bolt in which advance and return passages extend radially outward from respective circumferential grooves that extend radially outward from the valve bore. As a result, a rapid increase in flow occurs when the valve spool begins to open the circumferential grooves. The circumferential grooves provide increased flow by providing a greater flow area, thereby resulting increased phasing rates. However, the increased flow comes at the cost of decreased control stability of the camshaft phaser due to the rapid increase in flow which results from the valve lands of the valve spool opening an annular groove rather than individual passages as taught by Lichti.
What is needed is camshaft phaser which minimizes or eliminates one or more the shortcomings as set forth above.